Storage of high pressure gases and liquids is a critical requirement for many applications, e.g. rocket and aircraft propulsion components, automotive airbags, pneumatic and hydraulic systems, etc. The science for design and manufacture of suitable tanks for this purpose is well documented, with many examples of commercially available tanks. Typical tanks are made in the form of spheres or cylinders, and may be manufactured from metals or composite (with or without a liner).
Pictures of representative commercially available tanks for high pressure storage of gases and liquids are shown in FIG. 1 and FIG. 2 as examples of commercially available tanks. While such tanks are relatively common in large sizes with diameters in excess of six inches, they less common in the extremely small size-class (i.e. diameters of the order of a few inches). The problem is especially difficult in extremely weight sensitive applications (i.e. rocket engines), and in applications where the pressure of the stored fluid is very high (several hundred pounds per square inch).
The realization of small high-pressure tanks has proved challenging for several reasons including that, given a limitation of minimum gage thickness for conventional materials, the mass of the walls ends up being much higher than what is required, thereby making the tanks much heavier than they need to be and it is difficult to form conventional materials into suitable cylindrical or spherical shapes at the small scale. An exemplary conventional metal tank is welded together from pieces bent sheet metal. For example, a first sheet is rolled into a cylinder, and two hemispherical ends are then formed in a press. The hemispherical ends are then welded onto the ends of the cylinder. The smallest gage aluminum which can be worked in such a process is 30 mil, and even that is very difficult and expensive. This is the practical gage limitation that prevents conventional methods from making thinner-walled aluminum tanks. Consequently, there are currently no commercially available high tank factor storage tanks in the 1-10 cubic inch size class.
A key figure-of-merit commonly used in this context is the “tank factor” which is defined as: “Failure Pressure” times “Storage Volume” divided by “Tank Weight” (the lower the tank weight for a given failure pressure and volume, the better the tank, and hence, higher the tank factor). FIG. 3 depicts the tank factors for commonly available tanks as a function of storage volume, and clearly shows that while one can achieve high tank factors (nearing 30,000 meters for storage volumes in the 100-10,000 cubic inches range), the achievable tank factor decreases with size, there being no tanks with similar performance in the small size-scale (i.e. storage volumes of 1-10 cubic inches).
The tanks that do exist in the small size scale (less than 10 cubic inches) are either single-use disposable cylinders, for example, those used to inflate life-jackets, or “sample cylinders” used for capturing and transporting small samples of gas for analysis. These are limited to cylindrical shapes and have tank factors of less than 2500 meters.
Accordingly, it is desirable to manufacture a tank with a high tank factor (approximately 8,000 meters) in the 1-10 cubic inches volume range. In addition, it is desirable to devise a method of manufacturing such tanks that is effective and economical. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.